Hi...what is the new feature of iOS 14.5.1 software update...can I update it necessary....?

The iOS 14.5.1 update improve security content and also fixes an issue with App Tracking Transparency. Yes, you can update if you want. You can find all the detailed the information on the links below:

About the security content of iOS 14.5.1 and iPadOS 14.5.1 - Apple Support

About iOS 14 Updates - Apple Support

Apple security updates - Apple Support

Hope this helps and solves your question. Do not hesitate to ask if you need more information.

Since you are posting in the Business and Education Community, I will add to bodyxs's response to add that your administrator may restrict the ability to update, or have a policy in place deferring updates to a later time.